Setting multiple chip parameters using one IC terminal

ABSTRACT

A method for setting multiple chip parameters using one IC terminal is described. The chip comprises a first circuit coupled to the pin for setting a first parameter. A second circuit coupled to the pin sets a second parameter. In addition, a third circuit coupled to the pin sets a third parameter of the chip.

FIELD OF THE INVENTION

The present invention pertains to the field of integrated circuitdesign. More particularly, the present invention relates to a method toimprove cost efficiency by conserving integrated circuit terminals.

BACKGROUND OF THE INVENTION

Integrated circuit (IC) terminals are used to transfer input and outputsignals to and from a chip. These input and output signals may includedata, clock signals, and power terminals. Moreover, signals used tocontrol impedance, termination, slew rate, equalization, voltage swing,and reference voltages on the IC may be set and monitored through the ICterminals.

Packaging bumps or pins are examples of IC terminals. Whether bumps orpins are implemented depends primarily on the packaging technologychosen. Regardless of which packaging technology implemented, each ICterminal is typically used to set only one parameter of the IC. Forexample, a programming resistor that sets the impedance of a driver maybe set using a pin. Another pin may be used to set a reference voltagefor a differential receiver.

BRIEF DESCRIPTION OF THE DRAWINGS

The embodiments of the present invention are illustrated by way ofexample and not in the figures of the accompanying drawings, in whichlike references indicate similar elements and in which:

FIG. 1 shows a flowchart for setting multiple voltages on an integratedcircuit;

FIG. 2 shows on embodiment of a system for setting multiple chipparameters using a single IC terminal;

FIG. 3 shows one embodiment of a circuit for setting a first parameter;

FIG. 4 shows one embodiment of a circuit for setting a second parameter;and

FIG. 5 shows one embodiment of a circuit for setting a third parameter.

DETAILED DESCRIPTION

In the following detailed description, numerous specific details are setforth in order to provide a thorough understanding of the invention.However, it will be understood by those skilled in the art that thepresent invention may be practiced without these specific details. Inother instances, well-known methods, procedures, components and circuitshave not been described in detail so as not to obscure the presentinvention.

A method that allows a user to set multiple parameters of an IC througha single IC terminal helps to reduce costs by minimizing the number ofrequired IC terminals. If the IC terminals are predetermined, theability to set multiple parameters using a single IC terminal enablesmore parameters of the IC to be adjusted for circuit improvements. Forone embodiment of the invention, FIG. 1 shows a flowchart for settingmultiple variables using a single pin. In operation 100, a firstinternal circuit on an IC is coupled to an external circuit. The firstcircuit will be described in further detail below and in FIG. 3. Theexternal circuit may be a voltage source coupled to a voltage dividerthat comprises a first resistor and a second resistor. The externalcircuit may provide the first circuit with an input voltage. From themeasured input voltage and the known values of the first and secondresistors, the first circuit uses a first equation to calculate and seta first parameter in operation 110. The first parameter may be atermination resistance.

Next, in operation 120, a logic circuit or switch on the IC may be usedto couple a second internal circuit to the external circuit. The secondcircuit will be described in further detail below and in FIG. 4. Theexternal circuit may provide the second circuit with an input voltage.From the measured input voltage and the known values of the first andsecond resistors, the second circuit uses a second equation to calculateand set a second parameter in operation 130. The second parameter may bean equalization current.

Operation 140 determines if the user wishes to set a third parameter ofthe IC. If the user does not wish to set a third parameter, the processis terminated in operation 190. Otherwise, operation 150 couples a thirdinternal circuit of the IC to the external circuit. For this embodiment,a capacitor and a third resistor may be added to the existing voltagedivider structure. The third circuit will be described in further detailbelow and in FIG. 5. The external circuit may provide the third circuitwith an input voltage. Using the measured input voltage and the knownvalues of the first, second, and third resistors, the third circuit usesa third equation to calculate a variable in operation 160. The variablemay be a peak voltage value of the third circuit. The detected peakvoltage may be converted to a digital number using a translationcircuitry such as an analog-to-digital (A/D) converter. A thirdparameter may then be set in operation 170 using the digital numbergenerated by the A/D converter. For example, the digital number may seta slew rate (rise time) of an input/output (I/O) buffer. The I/O buffermay have a plurality of drivers of different sizes. The slew ratesetting of the I/O buffer may be adjusted by turning on drivers of aspecific size. Thus, the slew rate setting of the I/O buffer depends onwhich drivers are turned on by the digital number. Finally, the processis terminated in operation 190.

Because the external circuit is comprised of linear elements, theexternal circuit may be represented as a Thevenin voltage and resistancefor DC operation. The external circuit and the internal circuits form alinear network. Therefore, two variables may be used to set twoparameters. By measuring the network in two DC configurations, thevalues of the Thevenin voltage and resistance may be observed. The firstconfiguration may be achieved by operation 100 when the external circuitis coupled to the first circuit. The first circuit operated in opencircuit mode may provide the Thevenin voltage. The second situation maybe achieved by operation 120 when the external circuit is coupled to thesecond circuit. The second circuit operated in continuity mode mayprovide the Thevenin resistance. The derivations for the two parametersare described in further detail below.

To measure a third variable for setting a third parameter, an AC signalmay be applied to the linear network. Any capacitively coupled pathfunctions as an open circuit for DC signals. The third variable may bean effective Thevenin impedance when the AC signal is applied. Thederivation for the third parameter is described in further detail belowin equation

For another embodiment of the invention, the external circuit used toset the first, the second, and the third parameters of FIG. 1 arecoupled to the first, the second, and the third circuits through apackaging bump rather than a pin.

FIG. 2 depicts a system for setting multiple variables of an IC 200using a single IC terminal. The system comprises an external circuit210, a circuit to select parameter setting circuits 220, a firstparameter setting circuit 230, a second parameter setting circuit 240,and a third parameter setting circuit 250. Circuit 230, circuit 240, andcircuit 250 are used for setting a first, a second, and a thirdparameter of the IC. External circuit 210 is used to provide an input tocircuit 230, circuit 240, and circuit 250. The external circuit 210 iscoupled to the IC 200 through a single pin 205. Depending on thepackaging technology of the chip, pin 205 may be implemented as a bump.

Circuit 220 initially couples the external circuit 210 to the circuit230 to set the first parameter. After the first parameter has been set,circuit 220 then couples the external circuit 210 to circuit 240 to setthe second parameter. After the second parameter is set, circuit 220then couples the external circuit 210 to circuit 250 to set the thirdparameter.

For one embodiment of the invention, circuit 220 is a decoder. Foranother embodiment of the invention, circuit 220 is a counter. For yetanother embodiment of the invention, circuit 220 is a multiplexer.

For another embodiment of the invention, a first internal circuit may beused to set the first and second parameters and a second internalcircuit may be used to set the third parameter. For yet anotherembodiment of the invention, a first internal circuit may be used to setthe first, second, and third parameters.

FIG. 3 depicts an embodiment of the circuit 230 for setting a firstparameter of IC 200. The circuit 230 comprises a differential amplifier350, a termination resistor 340, and a circuit 360 for adjusting thetermination resistor based upon the output of the differential amplifier350. The differential amplifier compares an input voltage with areference voltage, xVcc. The input voltage is obtained from an externalcircuit such as a voltage divider comprising a DC voltage source (Vcc)310, resistor 320, and resistor 330. The value of the input voltage is afunction of Vcc 310, resistor 320, resistor 330, and resistor 340.

The magnitude of reference voltage, xVcc, may be a fraction of Vcc 310.The circuit 360 calculates and sets the termination resistor 340 suchthat the voltage drop across the termination resistor 340 isapproximately equal to xVcc. The following equation expresses therelationship between the voltage drop across the termination resistor340 and xVcc, wherein resistor 320 is R1, resistor 330 is R2, andresistor 340 is RT: $\begin{matrix}{{( \frac{R\quad 2\quad{}R\quad T}{{R\quad 1} + {R\quad 2{}R\quad T}} ){Vcc}} = {{xVcc}.}} & {{Equation}\quad 1}\end{matrix}$

Because the values for R1, R2, Vcc, and xVcc are known, RT is the onlyunknown variable and may be readily solved. Note that in order forcircuit 230 to function as a linear circuit, the termination resistor340 may be limited to a range of possible values defined by resistors320 and 330. Prior to circuit implementation, the range may bepredetermined by tests or simulations across different processes,temperatures, or voltages.

FIG. 4 depicts an embodiment of a circuit 240 for setting a secondparameter of IC 200. The circuit 240 comprises a differential amplifier450, a DC voltage source (Vcc) 480, a resistor 440, a current source470, and a circuit 460 for calculating and setting the current source470.

The resistor 440 is coupled to Vcc 480 and current source 470. Theresistance of resistor 440 is approximately equal or a known fraction tothe resistance of termination resistor 340 of circuit 230. Thus, aproper setting of termination resistor 340 also sets the resistor 440.The equalization current of the current source 470 is determined bycircuit 460. The circuit 460 is coupled to the differential amplifier450, which compares an input voltage with the voltage value at node M.The input voltage may be created by an external circuit. For example,the external circuit may comprise Vcc 310, resistor 320, and resistor330. For this embodiment of the invention, Vcc 310 is approximatelyequal to Vcc 480. The output of differential amplifier 450 is coupled tothe circuit 460. Circuit 460 sets the current source 470 such that thevoltage drop at node M is approximately equal to the input voltageprovided by the external circuit. Therefore, the following equation maybe derived, wherein resistor 320 is R1, resistor 330 is R2, resistor 440is RT, and the equalization current across current source 470 is leq:$\begin{matrix}{{( \frac{R\quad 2}{{R\quad 1} + {R\quad 2}} ){Vcc}} = {( {{Vcc} - {{RT}*{Ieq}}} ).}} & {{Equation}\quad 2}\end{matrix}$

RT was previously calculated in equation 1. Because the values for R1,R2, Vcc, and RT are known, leq is the only unknown variable and may bereadily solved. The constraint of RT, as previously discussed, may bealternatively described by the equation:RT*leq<Vcc−xVcc.  Equation 3

FIG. 5 depicts an embodiment of a circuit 250 for setting a thirdparameter of IC 200. The circuit 250 comprises a peak detection circuit560 coupled to slew rate setting circuit 565, resistor 540, and anexternal circuit. The resistor 540 is coupled to an AC voltage source550. The slew setting circuit 565 is coupled to an I/O buffer circuit505. The external circuit may comprise Vcc 310, resistor 320, resistor330, capacitor 570, and resistor 580.

The peak detection circuit 560 calculates a peak voltage at node P. Forone embodiment of the invention, voltage source 550 generates a pulsedsignal having a maximum voltage of 0.5*Vcc and a minimum voltage ofzero. Resistors 320 and 330 define the range of peak voltagesachievable. The fundamental frequency of the pulsed signal is largeenough so that the impedance of the capacitor 570 is sufficiently smallcompared to the resistors 320, 330, and 580. As a result, the followingexpression may apply, wherein resistor 320 is R1, resistor 330 is R2,the fundamental frequency of the pulsed signal generated by voltagesource 550 is w, and capacitor 570 is C: $\begin{matrix}{{R\quad 1},{{R\quad 2}\operatorname{>>}{\frac{1}{jwC}.}}} & {{Equation}\quad 4}\end{matrix}$Therefore, in an AC analysis, the resistor 580 appears in combinationwith resistors 320 and 330.

Because circuit 250 is a linear circuit that comprises both AC and DCcomponents, the peak voltage (Vp) at node P may be calculated usingsuperposition. Superposition involves algebraically adding the peakvoltage due to the DC (Vp1) and the AC (Vp2) voltage sources. To solvefor the DC equation, AC voltage source 550 is considered a short circuithaving zero impedance, while the capacitor 570 operates as an opencircuit having infinite impedance. The following equation may be derivedusing current analysis, wherein resistor 320 is R1, resistor 330 is R2,resistor 580 is R3, and resistor 540 is Rout: $\begin{matrix}{\frac{{Vcc} - {{Vp}\quad 1}}{R\quad 1} = {\frac{{Vp}\quad 1}{R\quad 2} + {\frac{{Vp}\quad 1}{Rout}.}}} & {{Equation}\quad 5}\end{matrix}$Equation 5 may be simplified and solved for Vp1 as follows:$\begin{matrix}{\frac{Vcc}{R\quad 1} = {{Vp}\quad 1( {\frac{1}{R\quad 1} + \frac{1}{R\quad 2} + \frac{1}{Rout}} )}} & {{Equation}\quad 6} \\{{{Vp}\quad 1} = {{{Vcc}( \frac{R\quad 2{}{Rout}}{{R\quad 1} + {R\quad 2{}{Rout}}} )}.}} & {{Equation}\quad 7}\end{matrix}$

To solve for the AC equation, the capacitor 570 is treated as a shortcircuit having zero impedance and Vcc is replaced by a short to ground.As stated above, the AC voltage source 550 fluctuates between zero and0.5Vcc. The following equation may be obtained using current analysis:$\begin{matrix}{\frac{{0.5{Vcc}} - {{Vp}\quad 2}}{Rout} = {{Vp}\quad 2{( {\frac{1}{R\quad 1} + \frac{1}{R\quad 2} + \frac{1}{R\quad 3}} ).}}} & {{Equation}\quad 8}\end{matrix}$Vp2 may then be calculated from equation 8: $\begin{matrix}{{{Vp}\quad 2} = {0.5{{{Vcc}( \frac{R\quad 1{}R\quad 2{}R\quad 3}{{Rout} + {R\quad 1{}R\quad 2{}R\quad 3}} )}.}}} & {{Equation}\quad 9}\end{matrix}$

The peak voltage, Vp, at node P may be obtained by adding Vp1 and Vp2:$\begin{matrix}{{Vp} = {{{Vcc}( \frac{R\quad 2{}{Rout}}{{R\quad 1} + {R\quad 2{}{Rout}}} )} + {0.5\quad{{{Vcc}( \frac{R\quad 1{}R\quad 2{}R\quad 3}{{Rout} + {R\quad 1{}R\quad 2{}R\quad 3}} )}.}}}} & {{Equation}\quad 10}\end{matrix}$

Once peak detection circuit 560 detects the peak voltage at node P, aslew rate setting circuit may set a rise time of a signal transmitted byI/O buffer circuit 505. The slew rate setting circuit may be implementedas a lookup table that determines the slew rate given a peak voltage.For one embodiment of the invention, a range of peak voltage values mapto a corresponding slew rate setting.

For another embodiment of the invention, the voltage source 550 maygenerate a maximum voltage value of 0.6*Vcc. The circuit 250, however,may have a limited feasibility voltage range for the voltage source 550in order to maintain its linear characteristics. The feasibility voltagerange may be a function of resistor 320, resistor 330, and resistor 540.The peak voltage is determined, in part, from resistor 580. As a result,the slew rate setting circuit 565 may define the feasible voltage range,which may thereby be used to determine a suitable value for resistor580. For example, if resistor 320 is 40 ohms, resistor 330 is 200 ohms,and resistor 540 is 50 ohms, the slew rate setting circuit 565 maydefine the feasible voltage range to be between 0.5Vcc and 0.7Vcc. If apeak voltage of 0.6Vcc is desired, then the user may choose resistor 580to be approximately 20 ohms based on equation 10.

Successive parameters may incorporate more reference errors due tocomponent tolerances. Therefore, it may be desirable to set the mostcrucial parameter first to minimize the programming components. The lesscrucial parameters may then be subsequently set.

In the foregoing specification the invention has been described withreference to specific exemplary embodiments thereof. It will, however,be evident that various modification and changes may be made theretowithout departure from the broader spirit and scope of the invention asset forth in the appended claims. The specification and drawings are,accordingly, to be regarded in an illustrative rather than restrictivesense.

1. A system, comprising: an external circuit; and an integrated circuit(IC) having an IC terminal, wherein the IC terminal couples the IC tothe external circuit, wherein the IC terminal is used to set a first anda second parameter of the IC, wherein the IC comprises a first circuitto determine the value of the first parameter, a second circuit todetermine the value of the second parameter, and a third circuit thatdetermines the value of a third parameter.
 2. The system of claim 1,further comprising: a switch, wherein the switch couples the firstcircuit to the external circuit to set the first parameter.
 3. Thesystem of claim 1, wherein the IC comprises an internal circuit thatdetermines the value of the first and second parameters.
 4. The systemof claim 1, wherein the first circuit comprises a differential amplifierthat compares a voltage as received at the IC terminal with a referencevoltage and generates an output value, wherein a logic circuit coupledto the differential amplifier sets the first parameter based on theoutput value.
 5. A method, comprising: coupling an external circuithaving a DC Thevenin equivalent circuit to a terminal of an integratedcircuit (IC); and using the Thevenin voltage and resistance of theexternal circuit to set two parameters in the IC, wherein the externalcircuit has an AC Thevenin equivalent circuit used to set a thirdparameter in the IC.
 6. A method, comprising: coupling a first resistorand a second resistor to a first circuit on an integrated circuit (IC)through an IC terminal; using the first circuit to set a first parameterof the IC; coupling the first resistor and the second resistor to asecond circuit on the IC through the IC terminal; and using the secondcircuit to set a second parameter of the IC.
 7. The method of claim 6,further comprising: setting the first parameter by solving an equationthat is a function of the first resistor and the second resistor.
 8. Themethod of claim 6, further comprising: setting the second parameter bysolving an equation that is a function of the first resistor, the secondresistor, and the first parameter.
 9. The method of claim 6, furthercomprising: coupling the first resistor, the second resistor, a thirdresistor, and a capacitor to a third circuit on the IC through the ICterminal; and using the third circuit to set a third parameter of theIC.
 10. The method of claim 9, wherein the third circuit uses a lookuptable to set the third parameter.
 11. An integrated circuit (IC),comprising: means for setting a termination resistance of the IC usingan IC terminal; means for setting an equalization current of the ICusing the IC terminal; means for setting a peak voltage of the IC usingthe IC terminal.
 12. An integrated circuit (IC), comprising: an ICterminal to couple the IC to an external circuit; and an internalcircuit coupled to the IC terminal, wherein the internal circuit sets afirst parameter and a second parameter of the IC, wherein the internalcircuit sets a third parameter of the IC.
 13. The IC of claim 12,wherein the first parameter is a termination resistance.
 14. The IC ofclaim 12, wherein the IC terminal is a pin.
 15. The IC of claim 12,wherein the IC terminal is a bump.
 16. An integrated circuit (IC),comprising: an IC terminal to couple the IC to an external circuit; andan internal circuit coupled to the IC terminal, wherein the internalcircuit sets a first parameter and a second parameter of the IC, whereinthe second parameter is an equalization current.
 17. An integratedcircuit (IC), comprising: an IC terminal to couple the IC to an externalcircuit; and an internal circuit coupled to the IC terminal, wherein theinternal circuit sets a first parameter, a second parameter and a thirdparameter of the IC, wherein the third parameter is a rise time.
 18. Anintegrated circuit (IC), comprising: a pin coupled to a first externalresistor (R1), a second external resistor (R2), and a voltage source(Vcc); a termination resistor (RT) coupled to the pin; a differentialamplifier coupled to the termination resistor, wherein the differentialamplifier has a reference voltage input (xVcc); and a first circuitcoupled to the differential amplifier, wherein the first circuit setsthe termination resistance such that the expression:[(R2*RT)/(R1*R2+R1*RT+R2*RT)]*Vcc=xVcc is satisfied.
 19. The IC of claim18, further comprising: a second circuit coupled to the pin, wherein thesecond circuit sets an equalization current (leq) of a current sourcesuch that the expression: [R2/(R1+R2)]*Vcc=Vcc−RT*leq is satisfied. 20.The IC of claim 19, further comprising: a third circuit coupled to thepin, wherein the third circuit sets a rise time of an input/outputbuffer circuit based upon a peak voltage (Vp) measured at the pin. 21.The IC of claim 20, wherein the Vp is obtained by adding a DC voltagecomponent and an AC voltage component.
 22. The IC of claim 20, whereinthe rise time as a function of Vp is set using a lookup table.
 23. TheIC of claim 20, wherein the rise time as a function of Vp is set using atranslation circuitry.
 24. The IC of claim 21, further comprising: acapacitor coupled to the pin; a third external resistor (R3) coupled tothe capacitor; and an internal resistor (Rout) coupled to the pin,wherein the expression:Vp=Vcc*[(R2*Rout)/(R1*R2+R1*Rout+R2*Rout)]+0.5Vcc*[(R1*R2*R3)/(R1*R2*R3+R1*R2*Rout+R2*R3*Rout+R2*R3*Rout)]is satisfied.